Serum Surfactant Protein D and Haptoglobin as Potential Biomarkers for Inflammatory Airway Disease in Horses

BACKGROUND: The identification of serum biomarkers of lung inflammation would facilitate the diagnosis of inflammatory airway disease (IAD) in horses. HYPOTHESIS: Horses with IAD have higher serum concentrations of markers of inflammation compared to controls. ANIMALS: Twelve horses with IAD and 10 control horses. METHODS: This was a prospective case–control study. Blood and BALF were collected from horses with IAD and controls. Serum concentration of surfactant protein D (SP‐D), haptoglobin, serum amyloid A (SAA) and of the soluble form of triggering receptor expressed on myeloid cells 1 (sTREM‐1) was measured using commercial ELISA tests. RESULTS: Horses with IAD had higher serum concentration (log‐transformed values) of SP‐D (mean ± SD: 1.773 ± 0.51), haptoglobin (6.657 ± 0.202) and SAA (0.128 ± 0.396) compared to controls (0.942 ± 0.226, 6.38 ± 0.22, −0.398 ± 0.319, respectively; P < .01 for all). Furthermore, the concentrations of SP‐D and haptoglobin combined allowed differentiating the 2 groups (IAD: 8.43 ± 0.564, controls: 7.322 ± 0.249, P < .0001) with a sensitivity and specificity of 100% when a cut‐off of 7.70 (log value) was employed. CONCLUSIONS AND CLINICAL IMPORTANCE: Surfactant protein D and haptoglobin serum concentrations could be a diagnostic aid in IAD. Further studies are necessary to establish the specificity of our findings before they can be applied in everyday practice.